My A/C was working last week perfect, then now, it won't even turn on the compressor. I am looking for a simple fix, or an easy test I can do.

The on /off switch works on the dash, because I can hear a small click under the dash like a relay making contact. However, the compressor doesn't even make a hint of trying to start.
The car has 120,000 miles, and I don't know the history because I just bought it in Feb of this year.
Like I said , it was working excellent last week, very cold air, no problems.

Thanks in advance.
Ian